Glass layers are widely used in microelectronic devices. As the integration density of microelectronic devices continues to increase, it is desirable to provide higher performance glass layers.
Glass layers may provide insulating layers for microelectronic devices. For example, insulating layers may be used for trench isolation and interlayer dielectric regions in microelectronic devices. As is well known to those having skill in the art, trench isolation techniques are used to isolate microelectronic devices in a microelectronic substrate by forming a trench in the microelectronic substrate, between devices, and filling the trench with an insulating material. In interlayer dielectric applications, a layer of insulating material is used to separate conductive layers (often referred to as "wiring layers" or "metalization layers") from one another and from the microelectronic substrate. Glass layers also may be used for gate dielectrics, capacitor dielectrics and other microelectronic applications.
In both trench isolation and interlayer dielectric applications, it may be desirable for the insulating material to exhibit high dielectric breakdown strength, low dielectric constant and loss, minimal chemical attack on adjacent films, ease of deposition and etching, low stress, low charge density and/or good chemical stability. Moreover, an insulating material should reflow at relatively low temperatures, so as to obtain smooth or planar layers that can reduce nonplanarities that may be introduced during microelectronic device fabrication. In addition, if multiple interlayer dielectric layers are employed, it may be desirable that such layers provide a softening point hierarchy, at least with respect to the final layer that is deposited at any given point in the process.
Many types of glasses have been used as insulating materials in microelectronic applications. For example, silicon dioxide (SiO.sub.2) has been used. Phosphosilicate glass (PSG) that incorporates phosphorus in the form of P.sub.2 O.sub.5 into the pure SiO.sub.2 material, has also been used. Borophosphosilicate glass (BPSG) that incorporates boron as B.sub.2 O.sub.3 into PSG has also been used. Each of these glasses may have various advantages and disadvantages.
Germanosilicate glass, which is a solid solution of silicon dioxide (SiO.sub.2) and germanium dioxide (GeO.sub.2), has also been investigated as an insulating material. For example, in U.S. Pat. No. 4,417,914 to Lehrer, a method is provided for depositing a thin film binary glass which has a softening or flow point far below temperatures at which glass is normally used in connection with integrated circuits flow. After the binary glass has been deposited on a semiconductor substrate, it is heated and reflowed. Preferably, the glass comprises a mixture of germanium dioxide and silicon dioxide, wherein the germanium dioxide is no greater than approximately 50 mole percent of the mixture. Phosphorus is added to the glass film for passivation of the underlying devices. See the Lehrer abstract.
Another use of germanosilicate glass for microelectronic devices is described in a publication by Ogino et al. entitled "A New Planarization Technique for LSI Fabrication Utilizing Si--Ge Film Oxidation", Japanese Journal of Applied Physics, Vol. 24, No. 1, January 1985, pp. 95-101. A new planarization technique in the LSI process using Si--Ge film oxidation is proposed. An Si--Ge film is deposited by the thermal decomposition of SiH.sub.4 and GeH.sub.4 and then oxidized in wet O.sub.2 ambient. During the oxidation, a large degree of fluidity appears below 800.degree. C., a temperature much lower than that needed for phosphosilicate glass flow. The oxide growth rate is more than one order of magnitude higher than that in crystalline Si. The oxide thickness decreases with increasing Ge content and oxidation temperature, owing to Ge evaporation. The planarization is also related to Ge evaporation. After the entire Si--Ge film has been oxidized, neither glass flow nor Ge evaporation occur, even at temperatures higher than that of the oxidation. The electrical properties of the Si--Ge oxide film are good enough for its use as an insulating layer. The film does not react with an underlying SiO.sub.2 or Si.sub.3 N.sub.4 layer. See the Ogino et al. 1985 abstract.
In a subsequent publication entitled "A Planarization Technique Utilizing Oxide Flow During H.sub.2 Treatment of a SiO.sub.2 --GeO.sub.2 Film", Japanese Journal of Applied Physics, Vol. 25, No. 7, 1986, pp. 1115-1120, Ogino et al. describe that a large oxide flow has been found to appear when a SiO.sub.2 --GeO.sub.2 mixed glass film is treated in a low-pressure H.sub.2 gas at 900.degree. C. Simultaneously, the greater part of the GeO.sub.2 component is evaporated. The flow mechanism is explained by the diffusion and evaporation of GeO molecules produced by GeO.sub.2 reduction. A planarization process utilizing this flow exhibits a large effect at low temperatures in comparison with phosphosilicate-glass flow. The oxide profile after a H2 treatment is no longer changed by a high-temperature treatment. The formed oxide is highly durable against acids. Electrical properties such as the dielectric constant, resistivity, and dielectric strength are comparable to those of a SiO.sub.2 film grown by the thermal oxidation of Si. The problem of a small amount of Ge crystallized on the bottom of the oxide layer is controlled by a decrease in the H.sub.2 pressure. See the Ogino et al. 1986 abstract.
Accordingly, germanosilicate glass holds promise for use in microelectronic devices as a potentially low reflow temperature layer with potentially high performance characteristics. It is also known that silicate glass can be doped with phosphorus and/or boron to further lower the reflow temperature thereof. However, notwithstanding this potential, there continues to be a need for improved methods of forming a layer of germanosilicate glass on a substrate and of using layers of germanosilicate glass in microelectronic devices.